To understand attrition analysis, one has to understand what attrition is. Attrition, in simple industry terms, is the number of people who quit the services of an organization voluntarily. Attrition analysis, therefore, is a method of finding out reasons as to why employees quit, what the contributing factors are, what could have been done by the organization to retain them, and what can be done to prevent future attrition for similar reasons.
To conduct attrition analysis, there has to be an exit interview or discussions (either formally or informally, but most organizations have a formal process for it). During exit interviews/discussions, every employee who is quitting the organization is asked about the reasons for leaving, what went well and what did not, and what the organization could have done to retain him/her.
When you compile the data of every employee who quit the organization over a period of time, you can identify the reasons and determine the major factors. Based on that information, you can conduct your analysis and recommend corrective and preventive actions.